The disclosure of the following priority application is herein incorporated by reference: Japanese Patent Application No. 2001-214601, filed Jul. 16, 2001.
1. Field of the Invention
The present invention relates to a microscope system which is equipped with a stage.
2. Description of Related Art
In a microscope which is equipped with an electrically driven stage, methods of setting the position of the electrically driven stage can broadly be classified into two categories.
The first method is an open loop control method. In this method, the rotational amount for the motor required in order to arrive at the target point is calculated in advance, and the motor is rotated based thereupon. Generally a stepping motor is used.
The second method is a closed loop control method. In this method, a sensor such as a linear encoder or the like is provided separately from the drive motor for detecting the position of the stage, and the motor is driven while comparing the present position with a target point, until the position of the target point is arrived at.
When setting the position of an electrically driven stage, generally the position upon the image monitor to which the observer has tried to shift, i.e. the so called xe2x80x98shift target positionxe2x80x99, and the position when the system has actually completed shifting, i.e. the so called xe2x80x98stage positionxe2x80x99, do not perfectly agree with one another. As a result, a minute error exists between these two positions. Even though the error between the shift target position and the stage position may be a minute amount upon the surface of the object under examination, if the observation magnification is great, this becomes a great difference upon the display means such as a monitor or the like, and it can happen that the field of observation intended by the observer is not necessarily always attained. For example, if the shift amount accuracy of the stage is xc2x110 microns with regard to the shift target position in case that the magnification of the objective lens is 100 and the size of the CCD is a third inch (diagonal dimension: 6 mm), the error amount is 0.01 mm upon the surface of the object. However, the error amount becomes 1 mm on the image-capturing surface of the CCD, which corresponds to a sixth of the diagonal dimension on the monitor. In particular, with an electrically driven stage which utilizes the above described open loop control method, its construction and control are simple and low in cost. However, since only the rotational amount of the motor is controlled, errors can easily occur due to backlash of the lead screw or the like when the rotational amount of the motor is converted to the shift amount of the stage, and it becomes difficult to enhance the accuracy of positioning. Due to this, errors can easily occur between the shift target position and the stage position.
On the other hand, with the above described closed loop control method, the position of the stage is detected in real time by the position detection sensor such as a linear encoder or the like, and it is possible to perform positioning while correcting the position of the stage until the difference from the shift target position is within a permitted range which is specified in advance. Due to this, it is possible to perform positioning at comparatively high accuracy. However, when a quite high positioning accuracy is demanded, so called hunting can take place in which the stage oscillates around the shift target position, since the permitted range described above is small. As a result the positioning may consume a considerable amount of time, and the phenomenon may even occur of the hunting continuing indefinitely.
The present invention proposes a microscope system which can display an image of the target position at high speed and with high accuracy.
A microscope system according to the present invention, comprises: a stage that shifts a specimen in x and y directions; a detection section that detects a position of the stage after shifting; a reception section that receives an input of a shift target position for the stage inputted by an observer; an optical system that forms a light flux into a focused and magnified image of the specimen; an image capturing section that captures the magnified image; and a shift section that, if the position detected by the detection section and the shift target position received by the reception section do not agree with one another, shifts a relative positional relationship between the light flux and the image capturing section.